Radiofrequency (RF) transmission structures utilize voltage-to-current (V2I) converters to convert a full-wave voltage input to a half-wave current output for transmission over an RF channel, such as wireless transmission. For example, Long-Term Evolution (LTE) utilizes one or more V2I converters during radio operations, such as transmission or reception of signals.
In an ideal (e.g., theoretical) case, the input of the V2I converter has a high impedance such that substantially no current flows into the V2I converter. The lack of current flow generates a virtual ground at the input, which causes the input to act as though it were coupled to ground (e.g., the voltage at the input is effectively zero for the purpose of calculating the current generated by one or more additional circuit elements). The virtual ground provides linearity to the V2I converter. Conventional V2I systems are unable to provide a virtual ground during a negative cycle of a full-wave input, resulting in non-linearity when the output waveform is close to zero. FIG. 1 illustrates one embodiment of a typical non-linear output of a V2I conversion circuit. Conventional V2I converters lack a good virtual ground, resulting in a current output 50 having a non-linear portion 52 when the voltage input signal is close to zero (e.g., transitioning to or from a negative cycle of the input voltage signal). The ideal waveform 54 is shown as a dashed line and represents a theoretical output wave free of non-linearity. Some conventional V2I systems can provide linearity within a narrow bandwidth, but cannot provide high linearity and high performance over a large bandwidth. Conventional V2I systems include process variations that result in the output signal falling below the quiescent current 56 of the V2I converter. Additional variations and non-linearity is introduced when the output signal falls below the quiescent current 56.